Some people may be more familiar with the name Dolichos lablab, which is a former name for the hyacinth bean. Now named Lablab purpureus, the hyacinth bean is a twining vine that can reach more that 30 feet in length in the tropics where it is never killed to the ground. In tropical areas it is a short-lived, herbaceous perennial. In my Zone 8b garden and other areas where freezing weather is a factor, it is grown as an annual and rarely grows more than 10 or so feet tall with a spread of 3 to 6 feet.
The hyacinth bean is assigned to the pea (Fabaceae) family by most taxonomists, but some place it in Papilionaceae. The plant has purplish green leaves, each with three leaflets (trifoliate). Each leaflet is 3 to 6 inches long and shaped like a broad oval or loose triangle.
Attractive bean-like flowers may be purple, white, rose, or reddish in color, and they are borne in racemes (a flower cluster in which the flowers are borne on short stalks along a long main stem). Following the flowers are the beans that are from 3 to 6 inches long and have the familiar flat, curved shape of butterbeans. On the purple selections beans and flowers are held out above the foliage by long, purple stems. The purple coloring is not present on the plants with white flowers.
Growing Hyacinth Bean
Hyacinth bean grows in almost any soil, including poor, acidic or alkaline. Performance is best in full sun, but adequate results can be had in a part sun location as long as the soil is well drained. Once established, it is very drought tolerant. Propagation is easy from seeds. If seeds are soaked overnight in water, germination is very quick. Beans take anywhere from 90 to 150 days to reach maturity but can be picked earlier for tender, cooked beans.
Uses of Hyacinth Bean
In many parts of the world, hyacinth bean is cultivated as a food plant. It is an important food source in tropical regions of Africa and Asia. In the United States, it is more likely to be grown as an ornamental. Reports are mixed as to its flavor. Like other members of the bean family, it fixes nitrogen, which makes it a good cover crop. It is also sometimes used as fodder for livestock.
While it is a great annual vine for covering trellises, walls, or fences, it has escaped cultivation and established in some natural areas, including south Florida, so caution is advised in tropical areas. The vine can clamber over the ground and make an effective groundcover, or it can be grown in containers or vegetable gardens.
All parts of the hyacinth bean can be eaten. The young beans can be boiled and eaten like other butterbeans, but they are reportedly very "beany" flavored. It is recommended that the dried seeds be boiled in two changes of water before they are eaten due to toxic levels of cyanogenic glucosides which can cause vomiting, difficulty breathing, and convulsions if large amounts are consumed. Young leaves can be eaten raw or in salads, and older leaves can be cooked like turnips or other greens. The flowers are an attractive and tasty addition to tossed salads, or they can be steamed. Tubers are produced that can be boiled or baked. The beans also make bean sprouts that are nutritious.
Not surprisingly, the handsome clusters of bright purple beans on long stems has value in the cut flower market. For this purpose, the stems are cut when all fruit on a stem is mature enough that the pod is swollen with its developing seeds. The stems last about 10 days in tap water treated with a floral preservative.
Two cultivars are widely grown as crops. ‘Highworth' from South India matures at an early age and has purple flowers and black seeds. ‘Rongai', originating in Kenya, is a late-maturing cultivar that has white flowers and light brown seeds. Other cultivars are also available that have been developed primarily for the ornamental plant industry, including selections that are dwarf or have other desirable or attractive attributes, such as red flowers or longer beans. Some are grown primarily for the pods while others are grown for the edible tuberous roots.
The value of the hyacinth bean as a crop is worth exploring in areas of the world where food shortages exist. It grows in almost any well-drained soil, and every part is edible. It could possibly improve the quality of life for many people. Most assuredly, it will add beauty to your garden that lasts throughout the summer season. Thanks to DonnaMack, Jules_jewel, morganc, and rylaff for the use of their images.